The present invention relates generally to a projection zoom lens and a projector apparatus using the same, and more specifically to a projection zoom lens for enlargement and projection of an image from a light bulb using a DMD (digital micro-mirror device) operable to select the direction of reflection of light, and a projector apparatus using the same.
So far, numerous projectors for enlarging and projecting images displayed on LCDs (liquid crystal devices) have been proposed. As well known in the art, DMDs comprising a micro-mirror array and operable to change the direction of reflection of light to form a display image toward a specific direction, too, are usable in place of LCDs.
A DMD, because it responds more quickly to control signals than does an LCD and is a reflection type device, is lower in the transmission loss of light quantity than a transmission type LCD. Therefore, when it comes to screen illuminance equivalent to that obtained through an LCD projector, a DMD projector is more favorable than the LCD projector, because the power of a light source unit can be lower, and a cooler used with it can be smaller in size and quieter than the LCD projector. In other words, if DMDs are used in lieu of LCDs, it would then be possible to provide a projector apparatus of far higher luminance and even smaller size.
In DMDs, however, the angle of rotation of the micro-mirror is set at ±12°. By a choice of this angle of rotation of the mirror, there is a switchover from reflected light (effective light) incident on a projection lens and used for projection to reflected light (ineffective light) not incident on the projection lens, and vice versa. Restrictions on the range of the angle of rotation place some limitations on where to locate an illumination optical system operable to enter illumination light into a light bulb in a DMD or the like and a projection lens operable to produce effective light; the illumination optical system and the projection lens must be proximate to the DMD in the same direction.
To stay away interference between the illumination optical system and the projection lens, there are some needs of reducing the diameter of a lens located in, and nearest to the reduction side of, the projection lens arrangement as much as possible, thereby ensuring that there is a large enough space (back focus) between the projection lens and the DMD, and implementing optical design in consideration of the fact that an optical member located near the DEM is used for both the illumination optical system and the projection optical system.
To address demands for size reductions of the projector apparatus, reductions of projection distance, an increasing degree of flexibility in location, cost reductions, and so on, various types of projection lenses contributing to size reductions, wide-angle arrangements, zooming arrangements and reductions in the number of lenses are now under study.
There are proposed several techniques of locating a convex lens (field lens) just before a DMD such that it is used not only for an illumination optical system but also as a part of a projection lens, thereby allowing the field lens to share a part of the aberration correction function of the projection lens. With such techniques, the whole optical system in the DMD projection apparatus can be made compact.